The present invention relates to plasma torches.
A plasma torch is a system which enables high pressure (around 500 MPa) gases to be generated by a high voltage (around 20 kV) electric discharge caused between two electrodes.
Plasma torches are used in industry, for example, to cut conductive materials, or to destroy certain products or materials, or to apply metal coatings. They are also used in the field of armaments to generate pressure enabling a projectile to be fired. U.S. Pat. No. 4,895,062, which describes a weapon employing a plasma torch, is an example of such use.
Known plasma torches comprise an anode and a cathode separated by a capillary tube made of a material which is both electrically insulating and likely to breakdown to generate a plasma (for example, a plastic material). The electrical discharge between anode and cathode is triggered by a copper fuse, or fuse made of another conductive material. The electric arc thus created produces a plasma which ablates the wall of the capillary tube thereby generating high pressure, high temperature, light gases.
These gases are used either to directly accelerate the projectile, or to vaporize a fluid (for example, water) enabling the gas volume to be increased.
In known plasma torches, the anode and cathode fixed on opposing sides of a support tube which ensures the rigidity of the torch and the radial confinement of the generated plasma.
The cathode is ring-shaped so as to enable the plasma jet to exit axially through the cathode.
As a result, during operation the pressure level at the anode is greater than that developed at the cathode.
In practical terms, pressures of around 400 MPa have been measured at the cathode against 600 MPa at the anode.
Such a difference in pressure has a negative effect upon the mechanical strength of the torch. It can also cause a deterioration of the sealing between the anode and the support leading to the emission of plasma jets from the anode out of the torch.